Those were the words that a senior F.B.I. agent texted in August 2016 to a colleague who was worried that Mr. Trump would win the election. For the president, that text seemed to validate his claim of a “deep state” conspiracy out to get him.

But the same inspector general report also undercut Mr. Trump’s narrative. Whatever the agent, Peter Strzok, meant, the F.B.I. did not “stop” Mr. Trump, nor did the inspector general find evidence it tried. To the extent that the F.B.I. and its director at the time, James B. Comey, did anything wrong in 2016, according to the report, it was to the disadvantage of Mr. Trump’s opponent, Hillary Clinton.

The sprawling report, the most comprehensive look back at the investigation into Mrs. Clinton’s use of an unclassified private email server, reflected a messier reality than the simple story line promoted by the White House: An array of senior officials at the F.B.I. and the Justice Department made mistakes, the inspector general determined, but he found nothing to conclude that anyone went easy on Mrs. Clinton or tried to harm Mr. Trump out of political bias.

If anything, the report affirmed the complaints that Mrs. Clinton and her team have lodged against Mr. Comey — that he went too far by criticizing her conduct while declining to bring charges, and that he erred by disclosing days before the election that he was reopening the inquiry while never revealing an investigation into contacts between Mr. Trump’s campaign and Russia.

“A fair reading of the report shows that the F.B.I. applied a double standard to the Clinton and Trump investigations that was unfair to Clinton and helped elect Trump,” said John D. Podesta, who was Mrs. Clinton’s campaign chairman. “That said, he’ll use one random Strzok email to spin a deep-state conspiracy which plays to his core.”

Any independent criticism of Mr. Comey — even though for his treatment of Mrs. Clinton — helps Mr. Trump undermine the credibility of someone who may be a crucial witness against him in any case of obstruction of justice arising from the president’s decision to fire the F.B.I. director last year.

It was Mr. Trump’s decision to fire Mr. Comey, who was then leading the investigation into contacts between Russia and the president’s team, that led to the appointment of the special counsel, Robert S. Mueller III.

“Any report which critiques former senior F.B.I. employees of both Robert Mueller and James Comey and are being used by Mueller as prime witnesses against President Trump is inherently a winner for the president,” said Sam Nunberg, a former Trump campaign adviser. “The I.G. report continues the delegitimization of the entire Mueller investigation, which is ultimately the fruit of the poisonous and disgruntled James Comey.”

Mr. Trump initially cited letters from his attorney general and deputy attorney general faulting Mr. Comey’s handling of the investigation into Mrs. Clinton as the reason for firing him. But the next day, the president acknowledged that he would have done it even without the letters and that he was thinking about the Russia investigation at the time.

More recently, his lawyer, Rudolph W. Giuliani, said one reason Mr. Trump fired Mr. Comey was that the F.B.I. director would not publicly exonerate the president in the Russia inquiry.

The report released Thursday did not examine the origins of the Russia investigation, which Mr. Trump has called into question. But it will be used to shape the perception of it.

Mr. Trump remained uncharacteristically quiet about the report in the hours after it was released, and his spokeswoman offered just a terse reaction to it.

“It reaffirmed the president’s suspicions about Comey’s conduct and the political bias among some members of the F.B.I.,” said Sarah Huckabee Sanders, the White House press secretary.

Jennifer Palmieri, who was the communications director for Mrs. Clinton’s campaign, said that “perversely” the report will help Mr. Trump on the margins by tarnishing the F.B.I.

“The report won’t move anyone who doesn’t already agree with Trump,” she said. “A nonbiased person can clearly see the F.B.I.’s actions only served to help Trump.”

Robert Bauer, who was White House counsel under President Barack Obama, said Mr. Trump will pick out findings he considers beneficial to his argument.

“How much this report helps Mr. Trump depends on how successfully in the short term he mischaracterizes its findings,” Mr. Bauer said. “But in the long run, the report stands as a conclusive rebuttal to his persistent claims that Hillary Clinton violated the law and escaped only because the investigation was somehow rigged.”

Yet while the report did not find that bias influenced the investigation, it did find that five F.B.I. employees assigned to the investigation into Mrs. Clinton expressed “statements of hostility toward then candidate Trump and statements of support for candidate Clinton.” Those employees “brought discredit to themselves” and “cast a cloud” over the investigation.

Among them was Mr. Strzok, the senior F.B.I. agent who sent the “we’ll stop it” text to Lisa Page, a senior F.B.I. lawyer. Mr. Strzok went from the Clinton investigation to the Russia investigation, but was moved off the case by Mr. Mueller last year after other political texts came to light. Ms. Page left her job this spring.

He sent her the “we’ll stop it” message after she texted him asking if Mr. Trump might really become president. Questioned by the inspector general, Mr. Strzok said that he did not remember the message but that it would have been meant to reassure Ms. Page that Mr. Trump would not win, not to indicate that he would use his job to influence the election.

Moreover, Mr. Strzok told the inspector general that if the F.B.I. were trying to harm Mr. Trump’s chances, it would have revealed its then-secret investigation into his campaign’s ties to Russia before the election, which it did not. The report further noted that Mr. Strzok and Ms. Page advocated more aggressive measures in the Clinton inquiry.

But allies of Mr. Trump said Mr. Strzok and other agents failed to follow up immediately on new emails found in fall 2016 on a laptop belonging to Anthony D. Weiner, the husband of an aide to Mrs. Clinton, because they were busy with the Russia investigation.

“Peter Strzok and the investigative team made a decision to go one direction which would be more damaging to this president than following up on other leads as it relates to Hillary Clinton,” Representative Mark Meadows, Republican of North Carolina, said on Fox News.

The F.B.I. delayed by several weeks looking into Mr. Weiner’s laptop. As a result, Mr. Comey’s announcement that he was reopening the email investigation came just days before the election and dominated the final days of the campaign.

In the end, the F.B.I. found nothing new on Mr. Weiner’s laptop that changed the decision not to charge Mrs. Clinton. But Mr. Strzok proved to be wrong. Neither he nor anyone else could stop Mr. Trump.

Follow Peter Baker on Twitter: @peterbakernyt.

A version of this article appears in print on , on Page A1 of the New York edition with the headline: Weapon for Trump, but It Cuts Both Ways. Order Reprints | Today’s Paper | Subscribe